Windham Weaponry is excited to offer it's newest multi-caliber AR-15 convertible upper assembly. This exciting new development will allow you a huge leap in modularity for your favorite rifle, the AR-15. We all know that the AR-15 has become the most popular sporting rifle in American history and this Kit allows you to get hands on with other popular calibers and expand your AR-15 horizons. This revolutionary upper is designed to allow you to switch between barrels with great ease. Typically this task would have been impossible if not for the brilliant engineers in the Windham Weaponry R&D department. If you have been considering dabbling in other AR-15 calibers pick up one of these Windham MCS kits and see how easy the transition can be.